Cathode ray tubes



Jan. 9, 1962 R. c. HERGENRoTHl-:R 3,016,474

CATHODE RAY TUBES Filed May ll, 1954 2 Sheets-Sheet 1 f @digg Jan. 9, 1962 R. c. HERGENROTHER CATHODE RAY TUBES 2 Sheets-Sheet 2 Filed May 1l, 1954 United States Patent() 3,016,474 CATHODE RAY TUBES Rudolf C. Hergenrother, West Newton, Mass., assignor to Raytheon Company, a corporation of Delaware Filed May 11, 1954, Ser. No. 428,945 12 Claims. (Cl. 315-13) This invention relates to a cathode ray tube and more particularly relates to a color television kinescope including an apertured electrode of increased aperture size which provides maximum fluorescent screen brightness,

`accurate color registry and low energy dissipation at said mask.

One of the most effective color kinescopes now in use comprises three electron guns, one for each primary color, a target electrode upon which said electron beams are adapted to impinge and an apertured electrically conductive plate, known as a shadow mask, which is positioned adjacent the target electrode and maintained at substantially the same potential as the latter. The target electrode includes a plurality of closely spaced triplets or groups of phosphor elements which, for example, may be Y of generally circular configuration or may take the form of parallel strips. Each phosphor element of a given group emits light of a different primary color when struck by electrons in a corresponding electron beam. The shadow mask of such tubes contains apertures of the same shape and size as the phosphor elements on the target. The number of apertures in the mask is equal to the number of groups of phosphor elements. The purpose of the shadow mask is to mask the electron beams so that the beam corresponding to a given primary color is prevented from striking those elements of the target corresponding to the other colors. The three electron guns corresponding to each of the color components are so arranged that `the beams from the guns are directed toward the shadow mask at different angles. At the mask the beams cross detail subsequently, this requirement results in a relativelyV small proportion of the total area of the mask being available for openings. This low fractional open area causes a relatively low fluorescent rtarget brightness, for a given electron beam current, and `a relative-ly high energy dissipation at the mask.

In accordance with this invention an electron accelerating voltage is applied between an apertured member known as an electron lens mosaic and the target, so that each aperture in said mosaic acts as a lens to converge the beam after passage through said corresponding aperture. By properly adjusting the accelerating voltage the electron spot size at the target can be made very small compared with the size of the openings in the shadow mask. In this manner the mask apertures may be made much larger in size than the phosphor element and the target brightness and system efliciency may be enhanced considerably.

A diicul-ty is encountered in some applications especially when comparatively high acceleratingvoltages are used, in that secondary electrons from the electron lens mosaic are pulled through the lens openings by the accelerating field and impinge upon the screen. These secondary electrons have random trajectories and do not focus on the same region or spot as the electrons coming 3,016,474 Patented Jan. 9, 1952 rice formed by inserting an apertured second or `auxiliary elec tron lens mosaic in close proximity with said first electron lens mosaic so that the apertures in both lens mosaics are in register and applying a relatively small voltage between the two lens mosaics such that a retarding field is presented to the secondary electrons. In one embodiment, the first electron lens mosaic is coated with an electrically insulating coating on one side and this coating is covered with an electrically conductive film or layer connected to a source of voltage positive or negative relative to said first electron lens mosaic, depending on whether the tilm is applied to the electron gun side or the target side, respectively, of the first electron lens mosaic. Alternatively, the auxiliary electron lens mosaic may be a separate'apertured electrodepositioned close to and in register with said first electron lens mosaic. By virtue of the close proximity of the two lens mosaics a strong retarding field for the secondary electrons may be obtained with a relatively low voltage and with only a negligible disturbance vof the trajectory of thev electrons originating from the electron gun. l

In the drawings, FIG. 1 is an enlarged fragmentary 1 View of a portion of acolor kinescope according to the invention including an electron lens mosaic and a target electrode and illustrating the beam focus effect;

FIG. 2 is an exaggerated fragmentary view illustrating the beam focusing effect in greater detail; i

FIG. 3 is a curve illustrating the relationship between the ratio of the radius of the electron lens mosaic aperture and the radius of the electron spot incident on the target to the ratio` of the voltages at the target and electron lens mosaic, respectively, taken relative to the cathode;

FIG. 4 is a schematic diagram of complete color kinescope embodying the invention;

FIG. 5 is a fragmentary View of the modification of the kinescope of FIG. 4 in which the electron lens mosaic and target electrode are curved;

FIG. 6 is a fragmentary view of a portion of a color kinescope including an auxiliary electron lens mosaic associated with the main electron lens mosaic for suppression of color dilution owing to secondary electrons;

FIG. 7 is a view of modification of the color dilution suppression system of FlG.v6 in which the two electron lens mosaics are two separately mounted electrodes; and

FIG. 8 is a view of a color dilution suppression system as applied to a color kinescope wh-ose compound electron lens mosaic contains longitudinal slits and whose target electrode is coated with phosphor strips arranged substantially parallel to said slits.

In FIG. l of the drawing is shown a portion of the kinescope 12 of FIG. 4. The kinescope 12 contains an evacuated envelope 14v which contains a plurality of electron guns 16, 17 and 18 in the neck of the envelope for supplying corresponding electron beams 20, 21 and 22,

The other terminal ofthe supply is connected to the electron beams.

`-in the plane of the electron lens mosaic.

ing more than avsingle aperture.

metalized film 35 of target electrode 28. An appropriate voltage for the electron lens mosaic 24 may be -obtained by means of potentiometer 41 shunting said supply. The

electron guns may be located so that their axes a-re parallel and equally distant from the central longitudinal axis of the electron gun assembly and spaced 120 degrees about the latter axis. The originally parallel electron beams,

`located 120 degrees apart about the axis of the electron gun assembly, are then converged at the apertures 25 in electron lens mosaic 24 by means of an electrostatic lens including a cylindrical grid 26, shown in FIG. 5, which is -common to all guns. Instead of using a lens system, however, the three beams may be brought together in a vplane of electron lens mosaic 24 by pointing the electron guns in the appropriate direction.

The ,target electrode 28 includes a rigid planar supporting member 30 consisting of glass, mica or other material capable of ktransmitting light. Deposited upon member 30 is a uorescent screen 31 consisting of a plurality of groups or triplets of circular phosphor elements or dots 33. These dots are capable of emitting red, blue and green light, respectively, as indicated by the color coding, when an electron beam impinges Vthereupon. Each group of three phosphor dots is oriented with respect to a corresponding aperture 25 in electron lens mosaic 24 so that each phosphor dot will lie in register with the beam corresponding to the color of light emitted from that dot, after focusing to be described later. The triplet associated with each electron lens mosaic aperture is displaced radially from each aperture in the electron lens mosaic by an amount proportional to the angle of incidence of the corresponding As yshown in FIG. 1, electron beams 2 0, 21 and 2,2 correspond, respectively, to the primary colors green, blue and red. The phosphor layer 31 is coated with an electron-transparent electrically conductive film 35 such asaluminum which may be applied by a process of evaporation under a vacuum. This electrically conductive phosphor backing serves as anelectrical conductor to which one terminal of the'source of high voltage 40 may be applied and further functions to produce increased light output, elimination of ion v bombardment of the phosphor layer and better contrast.

Although the groups of color elements so far described have been tertiary groups comprising the colors green, red and blue it should be understood that this invention is not limited to groups of any particular number or color emission.

The electron lens mosaic is made of an electrically 'conductive material, such as a copper-nickel alloy, and must be mounted so that it does not blend or warp in order that the electron beam paths continuously cross Asshown in FIGS. 1 and 2 the apertures 25 in electron lens mosaic 24 are circular corresponding to the circular configuration of the phosphor elements 33 of target 28.

Although a multi-gun kinescope has been described, the principles of this invention are also applicable to a single-gun kinescope.

In FIG. 2, is shown the convergence of a single one of the electron beams, such as `beam 20 of FIG. l, in the case 'of a three-gun kinescope, or the single beam from a Single-.gun kinescope, passing through an aperture 25 in an electron lens mosaic 24 maintained at a Positive potential. V1 with respect t0 the Common. cathin FIG. 2 as having a diameter equal to the diameter of the aperture 25 in the electron lens mosaic 24, the

' diameter of a practically realizable beam is larger than that of aperture 25 and the electron beams may each extend over a region of the electron lens mosaic includ- As shown inl FIG. 2, the yradius of aperture 25 in the electron lens mosaic 24 is denoted by r1 and the radius of the beam upon impingement on fluorescent screen 31 is denoted by r2.

It may be shown that the ratio of the radius of the aperture in the electron lens mosaic to the radius of the electron spot incident on the target screen for an axially symmetrical electric field is given by:

Although the electron beam of FIG. 2 is shown as being incident normal to the plane of the electron lens mosaic 24, Equation 1 is valid for other angles of incidence of theelectron beam.

YThe relationship Aof the ratio off iluorescent spot radius and the radius of the apertures of the electron lens mosaic to the ratio of the voltages V2 and V1, previously referred to, is 'shown in the curve of FIG. 3. This data is normalized at T2.. Zz... 7,1 1 when V1 l fail to reach the ltarget and Equation l becomes imagnary. As

exceeds 9 r2 increases in the negative direction which indicates that the electron beam has crossed over at the focuse before reaching the target.

It is thus evident that the diameter of the electron beam on striking the fluorescent screen may be made considerably smaller than the aperture diameter of the electron lens mosaic, the exact diameter being solely a function of the relative value of the voltages of the target electrode and electron lens mosaic, respectively, relative to a common reference potential such as that of the cathodes of the electron guns.

In kinescopes of the prior art using a shadow mask at the same potential as the target electrode, the opening in the shadow mask is restricted by the requirementl k that the projected electron spot on the fluorescent screen be no larger than one phosphor dot or element. The phosphor dot size is limited by the requirement that the various groups or triplets of phosphor dots should not overlap, and ideally, should just till the fluorescent screen. v

The fractional opening k of such apertured member is given by Y r is the radius of the aperture, and l is the center-to-center spacing of thev apertures.

where:

Tubes of the prior art such as described above have a maximum ratio of aperture diameter to aperture center-to-center spacing'of the order .of 0.4 which from Equation 2, gives a fractional open area of the electron lens mosaic of about 0.14. If the aperture diameter of the electron lens mosaic is doubled, the fractional open area will be quadrupled to a value of approximately 0.56, .resulting in a fourfold increase of the beam curlens mosaic. 'limiting the usable beam current, the average beam curi limiting values.

shown in FIG. -5.

those of the first electron lens mosaic. vsecurely interconnecting an electrically insulating layer or plate. between and in register with two electrically conductive layers or plates may, of course, be used. The electron lens mosaic 46 nearest the target electrode is .rent actually impinging upon the fluorescent screen of as shown in FIG. 3. This would result in a fourfold increase of fluorescent screen brightness for a given electron beam current. In addition, the fraction of the beam current intercepted by the electron lens mosaic would be lowered from 0.86 to 0.44, or almost halved, thereby substantially reducing the power dissipation at the electron If electron lens mosaic heating is the factor aforesaid increase of aperture size of the electron lens mosaic.

It `is also obvious that the electron beam voltage in the deflection coil field would then beonly'i the vfluorescent screen voltage, resulting in a reduced deflection field power requirement. The values of fractional opening just cited are merely illustrative and are not The theoretical limiting diameter of apertures 25 is obviously achieved when the ratio of aperture diameter to center-to-center spacing of the aper- 'tures is 0.5, corresponding to a fractional open area of 0.91. In practice, of course, the apertures may not be made this large since sufficient material must be left betweenapertures for satisfactory mechanical rigidity. The .fractional open area permissible when beam focusing of the type described in the subject invention isresorted to is considerably greater than that allowable with kinescopes of the prior art.

Although the kinescope heretofore shown and described utilizes a flat electron lens mosaic and a flat target electrode,the invention is also applicable to a kinescope ernu ploying a curved lens mosaic and target electrode, as

l of bulb and with the same beam deflection angle.

vOne difliculty encountered with the kinescope previously `described is that secondary electrons produced at l' the apertures of the electron lens mosaic are actedon by the accelerating eld between the lens mosaic and the target. Because of the random focusing of said second- 1ary electrons, the latter are not focused on the same areas of the fluorescent screen on which the primary electrons are focused and undesired areas of the fluorescent screen are excited, thereby resulting in color dilution. This difficulty may be prevented by means of the arrangement shown in FIGS. 6 and 7.

t In the tube of FIG.'6 a compound electron lens mosaic 44 is employed which consists of two-spaced electron lens mosaics 45 and 46 similar to lens mosaic 24 previously described. One of these electron lens mosaics is coated on one sideL with an electrically insulating coating 47,

applied as by evaporation under a vacuum. The other of the electron lens mosaics may be formed on the insulating coating 47 in the form of an electrically conductive layer, such as aluminum, applied as by evaporation under a vacuum thus havingits apertures in register with Any means of If such a curved structure is used the t fluorescent screen 31 may be deposited directlyl upon the curved end face 14` of the tube envelope 14 with an electrically conductive backing 35 superimposed on said .screen, in the manner shown in FIG.` 5. The electron connected to a negative voltage which may be of the order of from 20 to 100 volts relative to the other electron lens mosaic 45. The lower limit of the potential on electron lens mosaic 46 is the cathode potential. For example, electron lens mosaic 46 may be connected to the negative terminal of a unidirectional source of voltage 42 while the electron lens mosaic 45 is connected to the positive terminal of source 4Z. In one embodiment the potentials of the target electrode, electron lens mosaic 45 and electron lens mosaic 46, with respect to the cathode, were 20 kv., 5.1 kv., 5 kv., respectively. These values are merely illustrative, however, and the invention is not limited thereto.

Because of the close proximity of the two electron lens mosaics 45 and 46 of the compound electron lens mosaic 44 a strong retarding field for the secondary electrons leaving electron lens mosaic 45 is obtained between mosaics 45 and 46 with a relatively low voltage and only a slight disturbance of the trajectories of the electrons coming from the electron guns.

It should be understood that the aperturesin the respective electron lens mosaics 45 and 46 of FIG. 6 may be of any desired size or configuration within the limits previously set forth and consistent with the configuration of the color groups of the fluorescent screen. The details of the remainder of the kinescope of FIG. 6, as well as that of FIG. 7, to be described later, are otherwise similar to those shown in FIG. 4.

The target compound electron lens mosaic of FIG. 7 includes a pair of electron lens mosaics 45 and 46 supported separately within the tube envelope 14, rather than forming a single structure, as in case of the tube of FIG. 6. The apertures in the two electron lens mosaics, like those of the compound electron lens mosaic 44 of FIG. 6, must be in register. The unidirectional source 42 is connected between the two-apertured electrodes 45 and 46, as in the tube of FIG. 6. The separation `between the two electron lens mosaics may be of the order of the aperture radius but the optimum spacing will depend on the tube parameters.

.Instead of the electron lens mosaic of FIGS. l, 2 and 4, which contains a plurality of circular apertures, a twodimensional electron lens mosaic may be used whose apertures 25' take the form of longitudinal slits, as shown in FIG. 8. These slits may be formed by the space between adjacent ones of a plurality of parallel electricallyconductive strips 3S which, in the limiting case, consist of a series of wires. The fluorescent screen 31 of target electrode 28 of FIG. 8 comprises a multiplicity of groups of parallel phosphor strips or elements 33' which, in the usual kinescope, are arranged in color triplets. For example, strips 33' may be alternately red, blue and green light-emitting phosphors, as shown by the color coding in FIG. 8.

This electron lens mosaic also suffers from the aforesaid color dilution owing to secondary emission of electrons travelling toward the fluorescent screen. Undesirable color dilution may be eliminated by the addition of a closely spaced electron lens mosaic 56 placed parallel to electron lens mosaic 24 and positioned between the electron lens mosaic 24 and target electrode 28. This second electron lens mosaic 56 is positioned in register with electron lens mosaic 24 and is maintained at a potential which is negative with respect to electron lens mosaic 24 by an amount suflicient to provide a suitable retarding field in the region of the two electron lens mosaics.

Numerous other arrangements and modifications can obviously he devised readily by those skilled in the art, within the scope of the invention, as defined in the appended claims.

What is claimed is:

l. An electron discharge device comprising an evacuated envelope containing a target electrode adjacent one other end thereof and a compound electron lens mosaic positioned between said electron source and said target electrode adjacent and target electrode, said compound electron lens mosaic consisting of a first apertured electron lens mosaic and a second apertured electron lens mosaic spaced from and adjacent to said first electron lens mosaic, said first and second electron lens mosaics having apertures of substantially equal size, means for providing a unidirectional electron accelerating voltage between said compound lens mosaic and said target electrode for decreasing the cross-sectional area of each of said electron beams after passage through said apertures of said lens mosaic and prior to impingement upon said target, and means for maintaining a potential diiference between saidV -first Yandn second electron Ylens mosaicsfor producing a retarding field vin the region between said first and second electron lens mosaics.

2. An electron discharge device comprising an evacuated envelope containing a target electrode adjacent one end thereof, a source of electrons positioned adjacent the other end thereof and a compound electron lens mosaic positioned between said electron source and said target electrode adjacent said target electrode, said compound electron lens mosaic consisting of a first apertured electron lens mosaic and a second apertured electron lens mosaic spaced from and adjacent to said first electron lens mosaic, said target electrode including a fluorescent screen made up of a plurality of duplicate groups of phosphor elements of diierent color emission when impinged upon by electrons from said source said electron lens lmosaics each containing a plurality of apertures of greater size than said elements for permitting the passage therethrough of at least a portion of each of said electron beams to said target electrode, means for providing a unidirectional electron accelerating voltage between said compound lens mosaic and said target electrode for decreasing the cross-sectional area of each of said electron beams after passage through said apertures of said lens mosaic and prior to impingement upon said fluorescent screen, and means for maintaining a potential difference between said first and second electron lens mosaics for producing a retarding field in the region between said electron lens mosaics, thereby preventing secondary electrons emitted from said compound electron lens mosaic from reaching said target electrode.

3. An electron dischargedevice comprising an. evacuated envelope containing a target electrode adjacent one end thereof, an electron source positioned adjacent the other end thereof and a compound electron lens mosaic positioned between said electron source and said target electrode adjacent lsaid target electrode, said compound electron lens mosaic consisting of a first apertured electron lens mosaic and a second apertured lens mosaic spaced from and adjacent to said first electron lens mosaic, said target electrode including a fluorescent screen made up of a plurality of duplicate groups of phosphor elements of different color emission when impinged upon by electrons from said source said first and second electron lens mosaics containing a plurality of apertures arranged in a pattern corresponding to that of said groups ofV phosphor elements and being of greater size than said elements for permitting the passage therethrough of at least a portion of each of said electron beams to said target electrode, means for providing a unidirectional electron accelerating voltage between said compound lens mosaic and said target electrode for decreasing the cross-sectional area of each of said electron beams after passage through said apertures of said lens mosaic and prior to impingement upon said fluorescent screen, and means for maintaining the electron lens mosaic nearer said target at a potential negative with respect to the other of the electron lens mosaics for producing a retardl ing field in the region between said electron lens mosaics,

the potential difference between said mosaics being small as contrasted with the potential of each of said mosaics.

4. An electron discharge device comprising an evacuated envelope containing a target electrode adjacent one end thereof, a plurality of electron beam sources positioned adjacent the other end thereof and a compound electron lens mosaic positioned between said --electron sources and said target electrode adjacent said target electrode, said compound electron lens mosaic consisting of a first apertured electron lens mosaic and a second apertured electron lens mosaic spaced from and adjacent to said first electron lens mosaic, said target electrode including a fluorescent screen made up of a plurality of duplicate groups of phosphor elements of different color emission when impinged upon by electrons from said Y sources each of said groups containing Va number of phosphor elements equal to the number of electron beam sources, said first and second electron lens mosaics containing a plurality of apertures arranged in a pattern corresponding to that of said groups of phosphor elements and being of greater size than said elements for permitting the passage therethrough of at least a portion of each of said electron beams to said target electrode, the number of said apertures being equal to the number of said groups of phosphor elements on said fluorescent screen, said lens mosaic being so positioned relative to said electron beam sources and said target electrode that each of said beams is permitted to impinge upon a corresponding element of each of said groups, means for providing a unidirectional electron acceleratingy voltage between said compound lens mosaic and said target electrode forr decreasing the cross-sectional area of each of said electron beams after passage through said apertures of said lens mosaic and prior to impingement upon said fluorescent screen, and means for maintaining the electron lens mosaic nearer said target at a potential negative with respect to the other of the electron lens mosaics for producing a retarding field in the region between said electron lens mosaics, the potential difference between said mosaics being small as contrasted with the potential of each of said mosaics.

5. An electron discharge device comprising an evacutron lens mosaic and a second apertured electron lens` mosaic spa-ced from and adjacent to said first electron lens mosaic, said first and second electron lens mosaics having apertures Vof substantially equal size, said compound electron lens mosaic being positioned between said electron sources and said target electrode adjacent said target electrode, said target electrode including a uorescent screen made up of a plurality of duplicate groups .of phosphor elements of different color emission when impinged upon by electrons from said sources and an electron-transparent electrically conductive layer superimposed upon said fluorescent screen, said compound electron lens mosaic being so positioned relative to said electro'ngbeam `sources and said target electrode that each of said electron beams is permitted to impinge upon a corresponding element of said groups, means for maintaining the electron lens mosaic nearer said target electrode negative with respect l pingement upon said fluorescent screen by an amount dependent upon the magnitude of saidrvoltage, and means for maintaining the electronv lens mosaic nearer said-tar- Y get electrode negative with respect to the other electron lens mosaic for producing an electron retarding field in the region of said compound electron lens mosaic, the potential difference between said electron lensr mosaics being of such magnitude as to prevent secondary'elec trons emitted from said compound electron lens mosaic from reaching said target electrode without affecting substantially the electron beam trajectory.

6. An electron discharge device comprising an evacuated envelope containing a target electrode adjacent one end thereof, a plurality of electron beam sources positioned adjacent the other end thereof and a `compound electron lens mosaic consisting of a iirst electron lens mosaic and a second electron lens mosaic spaced from and adjacent to said first electron lens mosaic, said compound electron lens mosaic being positioned between said electron sources and said target electrode adjacent said target electrode, said target electrode including a lluorescent screen made up of a plurality of duplicate groups of phosphor elements of ditterent color emission when impinged upon by electrons from said sources and an electron-transparent electrically conductive layer super-imposed upon said iluorescent screen, each of said electron lens mosaics containing a plurality of apertures of substantially equal size, said apertures being of greater size than said elements and of substantially the same configuration as each of said elements for permitting the passage therethrough of at least a portion of each of said electron beams to said target electrode, means for maintaining said target electrode at a potential positive relative to said compound electron lens mosaic for causing said electron beams to converge after passage through said apertures of said compound electrode lens mosaic and prior to the impingement upon said iluorescent screen by an amount dependent upon the magnitude of said potential for producing a retarding eld in the region of said compound electron lens mosaic, thereby preventing secondary electrons emitted from said compound electron lens mosaic from reaching said target electrode.

7. An electron discharge device as set forth in claim 6 in which said target electrode and said electron lens mosaics are substantially at plates lying in planes parallel to one another and normal to the longitudinal axis of said device.

8. An electron discharge device as set forth in claim 6 in which said target electrode and said electron lens mosaics are curved plates having substantially the same degree of curvature.

9. An electron discharge device comprising an evacuated envelope containing a target electrode adjacent one end thereof, a plurality of electron beam sources positioned yadjacent the other end thereof and a compound electron lens mosaic consisting of a first electron lens mosaic yand a second electron lens mosaic spaced from and adjacent to said iirst electron lens mosaic, said compound electron lens mosaic being positioned between said electron sources and said target electrode adjacent said target electrode, said target electrode including a fluorescent screen made up of a plurality of duplicate groups of phosphor elements of different color emission when impinged upon by electrons from said sources and an electron-transparent electrically conductive layer superimposed upon said fluorescent screen, said elements in each of said groups being equal in number to the number of beam sources, each of said electron lens mosaics containing a plurality of apertures of substantially equal size, said apertures being equal in number to the number of said groups of phosphor elements and being of greater size than said elements for permitting the passage therethrough of at least a portion of each of said electron beam-s to said target electrode, said compound electron lens mosaic being so positioned relative to said electron beam sources and said target electrode that each of said electron beams is permit-ted to impinge upon a corresponding element of each of said groups, means for maintaining said electron lens mosaic nearer said target electrode at a potential negative relative to said target electrode for causing said electron beams to converge after passage through said l,apertures of said compound electrode lens mosaic and prior to the impingement upon said tluoressent screen by an amount dependent upon the magnitude of the potential difference between said target electrode and the electron lens mosaic nearer said target electrode, said electron lens mosaic nearest said target electrode being slightly negative with respect to the other of said electron lens mosaics for producing an electron retarding eld in the region of said compound electron lens mosaic, and means responsive lto said retanding field for preventing secondaryr electrons emitted from said compound yelectron llens mosaic from reaching said target electrode without substantially aifecting the electron beam trajectories.

10. An electron discharge device as set forth in claim 9 in which said target electrode and said electron lens mosaics are substantially lia-t plates lying in planes parallel to one another and normal to t-he longitudinal axis of said device.

'11. An electron discharge device as set forth in claim 9 in which said target electrode and said electron lens mosaics are curved plates having substantially the same degree of curvature.

l2. An electron discharge device comprising an evacu- -ated envelope containing a target electrode: adjacent one end thereof, Ia source of electrons positioned adjacent the other end thereof, and a compound electron lens mosaic comprising at least twoy individual apertured spaced-apart electron lens mosaics and being positioned between said electron source `and said target electrode, means for pro viding a unidirectional electron accelerating voltage beltween said compound lens mosaic and said target electrode, and means for producing a retarding eld in the region between said spaced-apart individual lens mosaics.

References Cited in the tile of this patent UNITED STATES PATENTS Re. 23,672 Okolicsany-i June 23, 1953` 2,315,367 Epstein Mar. 30, 1943 2,580,073 Burton Dec. 25, 1951 2,606,303 Bramley Aug. 5, 1952 2,611,099 Jenny Sept. 16, 1952 2,619,608 Rajchman Nov. 25, 1952 2,659,026 Epstein Nov. 10, 1953 2,669,675 Lawrence Feb. 16, 1954 i 2,690,518 Fyler et al. Sept. 28, 1954 2,692,532 Lawrence Oct. 26, 1954 2,710,890 Skellett June 14, 1955 2,728,024 Ramberg Dec. 20, 1955 2,734,146 Noskowicz Feb. 7, 1956 FOREIGN PATENTS 866,065 France Mar. 31, 1941 Patent Noo SQOlqllTll January 9g Rudolf CO Herqenrother It is hereby certified that error appears in the above numbered patent requiring correction `and. that the lsaid Letters Patent should read as corrected below.

Column 3v line 51W for blend read =e bend msg; column 4x, llne 42? for "lfoouxse"e read M fooule ===3 column Ti, line 2u for zmdn read w seid -mo Signed and sealed this 29th day of May 1962il (SEAL) Attest: l ERNEST w. swlDER DAVID L LADD tteeting Officer Commissioner of Patents UNITED STATES PATENT oEEIcE CERTIFICATE 0F CORRECTION' Patent Noo 39016)474 January 9(l M962 Rudolf C(7 Herqenrother pears in the abo've numbered pat- It is hereby certified that error ap nd that the -sad Letters Patent should ,read as ent requiring correction a corrected below.

for and read e .said --fo "olend" read me bend um; column column Iv line 2V Signed and sealed this 29th day of May 1962u (SEAL) Attest:

ERNEST w. swTDEE l DAVID L- LADD Commissioner of Patents Aiteang Officer 

